Removed invalid line from ReadTheDocs config.

The stable version of the documentation now won't build until I
release a new version of the game. Whoops ><

.readthedocs.yaml

@@ -20,6 +20,5 @@ formats:
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.8
   install:
   - requirements: docs/requirements.txt